LONDON — In the 25 years since she moved to London from her native New Jersey, Amy Lamé has staged a late-night manifesto on protected sex in one of the city’s most notorious gay cruising zones, and created and hosted a sex and sexuality-themed TV game show. She has also emceed a cabaret night whose guests have included a flame dancer, a hula hoop artist and a stripping dwarf.

Next up for Ms. Lamé: one of the most visible positions in London’s city government.

Sadiq Khan, the mayor of London, appointed Ms. Lamé in November as the city’s Night Czar, dedicated to fostering and promoting night life in the city. Belying its reputation as a world capital for food and entertainment, London has lost about 50 percent of its nightclubs and 35 percent of its locally owned and operated music spots since 2007. The city’s best loved clubs have had acrimoniouspublic fights with developers and residents to stay open.

Now, the mayor’s office is instituting measures — including the one-year appointment of Ms. Lamé — to ensure that London maintains its edge even as Britain’s exit from the European Union threatens the city’s status as Europe’s de facto capital of things like night life, tourism and banking.

“Sadiq could see night life disappearing before his eyes,” Ms. Lamé said at a recent dinner at a chic late-night restaurant in the Soho district. She had finished her martini — a passion fruit-flavored vodka, with a pour-over shot of champagne, served compliments of the house — and moved on to red wine. “My job is to stem that flow.”

Ms. Lamé, 46 and a self-described “chubby white American lesbian,” moved to London in 1992, looking for an adventure and a place to stretch her wings. She had just come out of the closet, and had graduated from Washington College on the Eastern Shore of Maryland with a degree in French and humanities with a specialty in medieval studies. (“Lots of jobs for French-speaking medievalists, by the way,” she said over dinner.)

New York seemed too close to home for a place to take the next step and, she said, like a place full of people from back home pretending they came from the city. So Ms. Lamé decamped to London and started working at First Out, a cafe-bar in Soho, which was then the city’s center of gay life.

While working there, she met Simon Casson, and in 1995 they started Duckie, a cabaret night and art collective that has run every Saturday for 22 years at the Royal Vauxhall Tavern. She began a wide-ranging freelance career that has included work as a presenter on BBC radio, a model, a game show host, a local activist and mayor of the borough of Camden. This spring, she will release her first book, a gay history geared toward children.

Ms. Lamé said she had never expected her far-ranging gigs to add up to a day job, let alone one sanctioned by the city government.

“It’s not a job that you can say: ‘When I grow up, I want to be a Night Czar, so I’m going to follow this path. I’m going to go into a degree in Night Czardom,’” Ms. Lamé said, breaking into a deep cackle.

The creation of the figurehead role, loosely based on models developed in other cities, including Amsterdam and Toulouse, France, is part of a broader effort by the mayor’s office to bolster night life in the city. In August, with support from the mayor, London began its long-awaited Night Tube, the first 24-hour subway service in the city, which runs on certain lines on weekends. That countered years of complaints about a public transportation network that, with the exception of night buses, virtually shuts down by 1 a.m.

Since then, Mr. Khan has come out in support of an “agent of change” principle that requires new developers who move in next to a music venue to take responsibility for soundproofing their buildings. The mayor has also started to lobby against soaring fees that venues have to pay to operate commercially.

The motives behind the push are clear. In an interview with the magazine Dazed in the run-up to his election last year, Mr. Khan said he didn’t want “young and creative Londoners abandoning our city to head to Amsterdam, to Berlin, to Prague, where clubs are supported and allowed to flourish.” The nighttime economy adds 26.3 billion pounds, or about $32.2 billion, to London’s annual economy, according to the mayor’s office.

Solving the problem has become an even bigger priority as the potential of a hard exit from the European Union looms and London’s young professionals and creatives — especially Continental natives — weigh the possibility of leaving for other capitals, where they can live without facing visa issues.

In her four months in the role, Ms. Lamé has taken on a variety of tasks largely centered on public appearances and media events. She holds nightlong meet-and-greets where she chats with night workers and night crawlers at pubs, homeless shelters, emergency care centers and other venues in some of the city’s less-trammeled districts. She lauds the benefits of London’s nighttime economy at events catering to club staff and night life mavens.

Late last year, Ms. Lamé appeared in a hard hat at a construction site to help draw attention to plans for a giant entertainment complex at Tottenham Court Road, near Covent Garden. Her most public success was helping negotiate the reopening of the famed Fabric, which shut after two teenage clubgoers died there after taking drugs.

Two city publicists accompanied her throughout our dinner, keeping an ear out from across the table to ensure that the interview didn’t fly off the rails. But Ms. Lamé’s off-kilter personality bubbled up throughout.

Conversation teetered from subjects like President Trump’s mental health to her infatuation with Benjamin Franklin. (“He was a creative genius, but he had the common touch, you know? He was a diplomat, but an inventor. He took risks.”) At one point on the way to dinner, Ms. Lamé slipped into a doorway of a building to, she joked, smoke crack.

This brashness has made for a sometimes rocky transition to politics. In November, days after her appointment, several right-wing city councilors wrote a letter calling for Ms. Lamé to set aside political bias, after they resurfaced several peppery posts on her personal Twitter account, including one that referred to politicians as “Tory scum” and another that appeared to celebrate Margaret Thatcher’s death. (She later issued an apology letter.)

Ms. Lamé does get clipped when the conversation turns to certain subjects, like the potential conflicts between her activist background and her political present; why she stayed in Britain; and the chance that London, a diffuse and relatively leafy capital dotted with neighborhood pubs that often shut by midnight, may never compete with night life hubs like Berlin and New York. She is a deep and abiding fan of the city, which she calls the best in the world.

And New York, Ms. Lamé said, “is resting on its laurels.”

“It needs to get its act together,” she added, “because we’re nipping at your heels.”

A version of this article appears in print on , on Page A4 of the New York edition with the headline: The (American) Life of London Parties, Now Out to Save Them All. Order Reprints | Today’s Paper | Subscribe